As mobile devices have been increasingly developed and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased as an energy source for the mobile devices. Among such secondary batteries is a lithium secondary battery having high energy density and discharge voltage, into which much research has been carried out and which is now commercially and widely used.
In general, a secondary battery is configured to have a structure in which an electrode assembly including a cathode, an anode, and a separator disposed between the cathode and the anode is mounted in a metal can or a battery case made of a laminate sheet in a stacked or wound state and an electrolyte is injected into the metal can or the battery case or the electrode assembly is impregnated with the electrolyte. Examples of the secondary battery with the above-stated construction include a cylindrical battery, a prismatic battery, and a pouch-shaped battery.
In recent years, much interest has been taken in a pouch-shaped battery configured to have a structure in which such a stacked or stacked/folded type electrode assembly is mounted in a pouch-shaped battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight, easy modification in shape, etc. In addition, the use of such a pouch-shaped battery has gradually increased.
Meanwhile, small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a battery pack having a plurality of battery cells electrically connected to each other because high output and large capacity are necessary for the middle or large-sized devices.
Preferably, the battery pack is manufactured so as to have as small a size and weight as possible. For this reason, it is necessary to provide a battery which can be stacked with a high integration. In recent years, a pouch-shaped battery, which has a small weight to capacity ratio, has been widely used. However, the pouch-shaped battery has lower extensibility than a prismatic battery when the pouch-shaped battery is assembled on a per module or pack basis. Conventionally, there has not been provided a structure that is capable of changing the pouch-shaped battery into the prismatic battery. As a result, it is difficult to manufacture a battery module or a battery pack using the pouch-shaped battery.
Furthermore, one of the important research problems is to improve safety of the pouch-shaped battery in addition to technology for changing the pouch-shaped battery into the prismatic battery in assembling on a per battery module or battery pack basis. For example, in a state in which an internal short circuit occurs in the secondary battery, in a state in which the secondary battery is overcharged with higher than allowable current and voltage, or in a state in which the secondary battery is abnormally operated due to exposure to high temperature, falling, or deformation caused by external impact, the electrolyte in the secondary battery is decomposed with the result that high-pressure gas is generated. The generated high-pressure gas may deform the battery case and shorten the lifespan of the battery. According to circumstances, the battery may be combusted or explode.
In order to prevent combustion or explosion of the battery when the high-pressure gas is generated and to efficiently discharge the gas, a structure in which the battery cell case is provided with a vent member configured to be ruptured when the pressure in the battery reaches a predetermined level for discharging the gas out of the battery cell, thereby preventing explosion of the battery cell has been used. However, the gas discharged from the battery cell contains toxic components. As a result, humans may be injured by the gas discharged from the battery cell.
Therefore, there is a high necessity for a battery cell configured to have a structure that is capable of improving extensibility in assembling on a per battery module or battery pack basis while exhibiting all advantages of the pouch-shaped battery and improving safety of the pouch-shaped battery.